Greetings from South Carolina :-) Warrior_For_Christ
It has been my experience within RC that you can mount engines larger that what the kit calls for. Engines are based on wingspan if I were going to put an engine on this plane I would attempt to put just a little larger motor than what the kit calls for provided it would balance out properly.

If you have already built this airplane I would remove all the electronics and find the largest engine that I could mount that does not take away from the looks and then put in the electronics temporarly and check the balance then.